(56+1)x56分之3=56x56分之3+56分之3=3又56分之3
57x3/56=(56+1)x3/56=56x3/56+1x3/56=3+3/56=3 3/56
57乘56之3=（56+1）×56之3=56×56之3+1×56之3=3+56之3=3又56之3
3又56之3
